This invention relates generally to film cooled combustor liners for use in gas turbine engines and more particularly to such combustor liners having regions with closely spaced cooling holes.
A gas turbine engine includes a compressor that provides pressurized air to a combustor wherein the air is mixed with fuel and ignited for generating hot combustion gases. These gases flow downstream to one or more turbines that extract energy therefrom to power the compressor and provide useful work such as powering an aircraft in flight. Combustors used in aircraft engines typically include inner and outer combustor liners to protect the combustor and surrounding engine components from the intense heat generated by the combustion process. A variety of approaches have been proposed to cool combustor liners so as to allow the liners to withstand greater combustion temperatures. One such approach is multi-hole film cooling wherein a thin layer of cooling air is provided along the combustion side of the liners by an array of very small cooling holes formed through the liners. Multi-hole film cooling reduces the overall thermal load on the liners because the mass flow through the cooling holes dilutes the hot combustion gas next to the liner surfaces, and the flow through the holes provides convective cooling of the liner walls.
Various phenomena commonly occurring in gas turbine combustors can reduce the cooling film effectiveness and bring hot gases next to the liner surfaces. One such condition is swirl impingement, which is caused by swirlers located in the fuel nozzles to promote better combustion. The swirl of the combustion flow induced by the swirlers causes hot gases to impinge against the liners. Swirl impingement is typically confined to distinct regions on the liner surfaces, which are a function of the combustor design. These regions will experience a loss of cooling film effectiveness and thus be more susceptible to thermal degradation. Another cause of reduction in cooling film effectiveness is the presence in the combustor liners of dilution holes, borescope holes, igniter port holes and the like. Because such holes are considerably larger than the cooling holes, the wake produced by the influx of air through these larger holes will disrupt the cooling film behind them. Thus, regions of the liners immediately downstream of dilution and other liner holes will also be prone to a loss of cooling film effectiveness.
Accordingly, there is a need for a combustor liner in which cooling film effectiveness is increased in the areas of the liner that are otherwise susceptible to a loss of cooling film effectiveness.